It is known to form graphic patterns on substrates using transfer articles bearing predesignated designs. G.B. Patent No. 1,218,058 (Hurst et al.) discloses transfers with an adhesive layer applied to only those areas intended to be transferred to the substrate. U.S. Pat. Nos. 4,7.86,537 (Sasaki) and 4,919,994 (Incremona et al.) disclose transfer graphic articles wherein the graphic design is formed via imagewise differential properties within the transfer film itself. One problem with such approaches is that a large and varied inventory must be maintained in order to provide a variety of graphic patterns.
Hot stamping foils comprising a carrier, one or more color layers, and an adherence layer have been known for some time. Such films have been used to provide imagewise graphic patterns, e.g., alphanumeric or decorative legends, to substrates. In some embodiments, additional members such as release layers are used to facilitate desired performance. In some embodiments, so-called "texture layers" and/or "ticks", metal layers, etc. are used as well to yield desired appearance. Hot stamping foils are also sometimes called hot stamp tapes or thermal transfer tapes.
To form a graphic pattern on a desired substrate, the adherence layer of the transfer film is contacted to the substrate and heat applied in imagewise fashion to the carrier. This leads to bonding of the adherence layer to the substrate where heat was applied. The carrier is then removed, resulting in selective separation of the color layer(s) therefrom in the region or regions corresponding to the image in which the heat was applied. The carrier and non-heated portions of the color layer(s) and adherence layer are removed from the substrate leaving the desired graphic pattern thereon. The color layer(s), adherence layer, and any other layers that are selectively applied to the substrate should split or fracture in desired manner in order for the applied graphic pattern to have a desired edge appearance.
Some illustrative examples of previously known hot stamping foils are disclosed in U.S. Pat. Nos. 3,770,479 (Dunning) 3,953,635 (Dunning), and 4,084,032 (Pasersky).
It has also been known to transfer graphic patterns using means in addition to or other than heat to achieve imagewise separation of imaging material from a carrier and adhesion to a substrate. For example, U.S. Pat. No. 3,834,925 (Matsumura et al.) discloses a transfer material that utilizes solvent action to achieve imagewise deposition.
An advantage of the foregoing techniques is that the transfer film may be made as a uniform sheet, i.e., with no specific latent image embodied therein. The applicator defines the graphic pattern by controlling the application process, e.g., imagewise application of heat. This permits the maintenance of a smaller inventory of material.
One well known use of hot stamping foils is to print legends on vehicle identification plates. For example, license plates produced using hot stamping foils have been used in Austria, Australia, Finland, Germany, Ireland, Portugal, and Switzerland. One commercially available hot stamping foil currently used on license plates with polyvinyl chloride cover films is believed to comprise a polyester carrier, about 28 microns thick; a color layer based on acrylic resins such as polymethyl methacrylate and containing carbon black pigments, about 5 microns thick; and an acrylate-based adherence layer, about 5 microns thick. Examples of resins that are believed to have been used in adherence layers include polyvinyl alcohol copolymers, nitrocellulose, and methyl methacrylate/butyl methacrylate copolymers.
Recently improved retroreflective sheetings have been made available which have cover films made of olefin-based materials or polyurethane-based materials to improve certain performance. As disclosed in U.S. Pat. No. 4,896,943 (Tolliver et al.), olefin-based cover films, e.g., ethylene/acrylic acid copolymers, can provide superior properties including abrasion and dirt resistance. Conventional hot stamping foils do not achieve good adherence to such cover sheets, however, resulting in graphic patterns having unsatisfactory durability and performance. The need exists for improved hot stamping foils which can be used to form durable graphic patterns on such cover sheets and a method for forming such graphic patterns.